Molten metal, particularly molten aluminum, in practice generally contains entrained solids which are deleterious to the final cast metal product. These entrained solids appear as inclusions in the final cast product after the molten metal is solidified and cause the final product to be less ductile or to have poor bright finishing and anodizing characteristics. The inclusions may originate from several sources. For example, the inclusions may originate from surface oxide films which become broken up and are entrained in the molten metal. In addition, the inclusions may originate as insoluble impurities, such as carbides, borides and others or eroded furnace and trough refractories.
Porous ceramic foam materials are known to be particularly useful in filtering molten metal, as described in U.S. Pat. No. 3,893,917 for "Molten Metal Filter" by Michael J. Pryor and Thomas J. Gray, patented July 8, 1975, and also as described in U.S. Pat. No. 3,947,363 for "Ceramic Foam Filter" by Michael J. Pryor and Thomas J. Gray, patented Mar. 30, 1976 and U.S. Pat. No. 4,081,371 for "Filtering of Molten Metal" by John C. Yarwood, James E. Dore and Robert K. Preuss, patented Mar. 28, 1978, all of which are assigned to the assignee of the instant invention and incorporated herein by reference.
These ceramic foam materials are particularly useful for filtering molten metal for a variety of reasons included among which are their excellent filtration efficiency, low cost, ease of use and ability to use same on a disposable, throwaway basis. The fact that these ceramic foam filters are convenient and inexpensive to prepare and may be used on a throwaway basis requires the development of means for easily and conveniently assembling and removing porous, molten metal filters from a filtration unit while providing a highly efficient filtration assembly. Since the filters are designed to be a throwaway item, it is essential to provide an effective means of sealing the filters in place in its holder which is easy to assemble, disassemble and clean up. The holder or filter chamber itself is normally an integral part of a trough, pouring pan or tundish, etc. and should be constructed of refractory materials resistant to the molten metal similar to those used in standard trough construction. It is greatly preferred to seal the filter plate in place using a resilient sealing means or gasket type seal peripherally circumscribing the filter plate at the bevelled portion thereof. The gasket type seals ensure a leak free installation and also provide an effective parting medium which is essential for ease of disassembly. In addition, since the gaskets or sealing means prevent ingress of metal to the sealing faces of the holder unit, their use considerably eases clean up and effectively prolongs the life of the unit by eliminating problems of metal attack. Furthermore, because of its resiliency, the gasket may provide sufficient frictional force to hold the filter body in place in the holder or filter chamber without resorting to other types of hold down devices. The resilient sealing means should be non-wetting to the particular molten metal, resist chemical attack therefrom and be refractory enough to withstand the high operating temperatures.
Heretofore, the ceramic foam filters were gasketed with pre-cut strips of low density ceramic fiber having an organic binder. The straight pre-cut strips were simply taped to the bevelled edges of the filters after the filter had been baked and fired. As a result of the foregoing process, a number of disadvantages arose. Firstly, as the gasket is merely taped to the filter the fit is relatively loose and thus the gasket can be easily damaged during handling of the filter. Secondly, since the pre-cut strips are straight and the edges of the filter which are to be sealed are bevelled, a misfit occurs which in some cases results in the molten metal passing between the gasket and filter plate. Finally, as the gasket material is not taped to the filter until after it is fired, the filter must be dressed, that is coating the edges with additional ceramic slurry, in order to insure that the edges of the filter are not directly handled during further processing.
Naturally, it would be highly desirable to develop a process for integrally bonding a gasket onto a ceramic foam filter which overcomes the above-noted disadvantages.
Accordingly, it is a principal object of the present invention to provide an improved method and apparatus for integrally bonding a gasket seal onto a ceramic foam filter used in the filtration of molten metal.
It is a particular object of the present invention to provide an integrally bonded gasket on a ceramic foam filter which uniformly seats on the bevelled edges of the filter.
It is a still further object of the present invention to provide improvements as aforesaid which are convenient and inexpensive to utilize and which result in improved sealing of the filter in the filter chamber.
Further objects and advantages of the present invention will appear hereinbelow.